1. Field of the Invention
The present invention relates to a method and a device for distributing liquid fuel in a fluidized bed from below through substantially vertical risers extending through a constriction plate for the supply of fluidizing and primary air, the fuel being carried up through the risers by a gaseous driving agent and out through distribution openings.
Certain difficulties have been encountered in the supply of oil and other liquid fuels to incinerators employing fluidized beds, because there is a tendency for distribution or supply openings or atomization nozzles to be blocked by carbonization and sintering of the fuel. Also it has been found difficult to distribute the fuel uniformly over the entire fluidized bed.
2. Description of the Prior Art
These problems are solved, at least in part, by an oil supply system which is described in CA Pat. No. 987 100. In this system a double constriction plate is employed, so that between the upper and the lower walls of the constriction plate an oil supply chamber is formed which communicates with each of the tuyeres supplying fluidizing and primary air to the fluidized bed of the incinerator. Each tuyere is of relatively large cross section to allow the passage of the required quantity of fluidizing air, and transportation of oil up through the tuyeres is stated to take place along the internal walls of the tuyeres, on which is formed an oil film which "climbs" up the tuyeres due to the flow of air.
However, a disadvantage of the system shown in CA Pat. No. 987 100 is that the double constriction plate with tuyeres constitutes a complicated structure which is not easily accessible for maintenance. This is especially true for the apertures between the oil chamber in the constriction plate and the tuyeres, which may easily be blocked. Furthermore, it is a disadvantage that rapid cutting off of the fuel supply can only be achieved by cutting off the supply of fluidizing air, so that fluidizing cannot be maintained after the fuel supply has been cut off.
According to U.S. Pat. No. 4,021,193 the fuel may be distributed in the fluidizing air through separate nozzles immediately ahead of the opening through which the fluidizing air is introduced in the bed. This allows the fuel supply to be cut off while continuing the supply of fluidizing air. However, the nozzles through which the fuel is introduced in the fluidizing air passage, are adjacent the combustion bed. This fact as well as the fact that the pressure of the fluidizing air is low, as in the structure according to CA Pat. No. 987 100, result in a tendency of the fuel to form deposits, eventually blocking the inlet openings for fuel and fluidizing air, at least in an ordinary fluidized bed as contrasted with a spouted fluidized bed with which the U.S. Pat. No. 4,021,193 is actually concerned.